Discharge electrode, RF plasma generation apparatus using the same, and power supply method

Abstract

A plurality of electrode bars are arranged in parallel with each other, and side electrode bars are connected to the corresponding opposite ends of the electrode bars, thereby forming a ladder-like RF discharge electrode. Power supply points are arranged axisymmetrically with respect to a reference line, which is a bisector which bisects one side of the RF discharge electrode, while being spaced a predetermined distance from the reference line, thereby suppressing voltage distribution on the ladder electrode, which has an effect on uniformity of discharge distribution, to a sufficiently low level of nonuniformity. Thus, uniform distribution of film deposition rate can be obtained, thereby enabling uniform deposition even in large-area applications.

What is claimed is:  
     
       1. A discharge electrode of an RF plasma generation apparatus to which power is supplied from an RF power source through a matching unit, wherein the discharge electrode is of a ladder type or grid type having a power supply portion with at least two RF power supply points of substantially equal voltage. 
     
     
       2. A discharge electrode according to  claim 1 , wherein two groups of electrode bars, each group comprising a plurality of parallel electrode bars, are arranged perpendicular to each other; and the RF power supply points are arranged axisymmetrically with respect to a bisector which bisects sides of the RF discharge electrode. 
     
     
       3. An RF plasma generation apparatus in which a discharge electrode and substrate support means are disposed in parallel with each other within a reaction chamber, and RF power is supplied to the discharge electrode from an RF power source through a matching unit, wherein a discharge electrode according to  claim 1  is used for the discharge electrode. 
     
     
       4. An RF plasma generation apparatus according to  claim 3 , wherein the power supply portion is located in a peripheral portion of the discharge electrode which does not face a substrate. 
     
     
       5. An RF plasma generation apparatus according to  claim 3 , wherein power transmission lines extending from the matching unit to the corresponding power supply points are of the same length. 
     
     
       6. An RF plasma generation apparatus according to  claim 3 , wherein a transmission line is connected to the power supply portion of the discharge electrode such that an uninsulated bare metallic connector for connecting the power supply point and a power line of the transmission line has a diameter at least equal to that of the electrode bar as measured in the vicinity of the power supply portion. 
     
     
       7. An RF plasma generation apparatus according to  claim 3 , wherein the distance between the power supply point and a metallic terminal member of a grounding line of a transmission line is at least 1 cm. 
     
     
       8. An RF plasma generation apparatus according to  claim 3 , wherein a transmission line is attached to the discharge electrode from opposite the substrate support means at an angle of at least 45° with respect to the discharge electrode. 
     
     
       9. An RF plasma generation apparatus according to  claim 3 , wherein the shortest distance between a metallic portion of a power line of a transmission line and a grounded member is at least 1 cm. 
     
     
       10. An RF plasma generation apparatus according to  claim 3 , wherein a metallic connector of the power supply portion of the discharge electrode is covered by an insulator having an outside diameter of 10 mm to 40 mm. 
     
     
       11. An RF plasma generation apparatus according to  claim 10 , wherein a gap between an outer circumferential surface of the metallic connector and an inner circumferential surface of the insulator is not greater than 3 mm. 
     
     
       12. An RF plasma generation apparatus according to  claim 3 , wherein a structure for power supply to the discharge electrode is an insulated structure such that a transmission line is connected to the discharge electrode by means of a connector and a receptacle in such a manner that a radial gap between an external shield and a core conductor within the interior of the connected connector and receptacle is not greater than 3 mm. 
     
     
       13. An RE plasma generation apparatus in which a discharge electrode and substrate support means are disposed in parallel with each other within a reaction chamber, and RF power is supplied to the discharge electrode from an RF power source through a matching unit, wherein the number and position of power supply points on the discharge electrode are determined such that the shortest distance as measured along the discharge electrode between at least one of the power supply points and any point located within a portion of a surface of the discharge electrode which faces a substrate is not greater than one-fourth of the in-vacuum wavelength of the RF power. 
     
     
       14. An RF plasma generation apparatus in which a discharge electrode and substrate support means are disposed in parallel with each other within a reaction chamber, and RF power is supplied to the discharge electrode from an RF power source through a matching unit, wherein in order to supply RF power to a plurality of points, the RF plasma generation apparatus comprises, as a power transmission line, a first coaxial cable for receiving an output from the RF power source and having an end divided to form two ends; two second coaxial cables connected to the divided ends of the first coaxial cable, each of the second coaxial cables having a length equal to one-fourth of an in-cable wavelength of the RF power and a characteristic impedance equal to that of the first coaxial cable, and having an end divided to form two ends; and four third coaxial cables, each connected to a divided end of the second coaxial cables and having a characteristic impedance equal to that of the first coaxial cable. 
     
     
       15. An RF plasma generation apparatus according to  claim 14 , wherein the coaxial cable serves as a distributed constant line. 
     
     
       16. A power supply method for an RF plasma generation apparatus in which a ladder-type or grid-type discharge electrode and substrate support means are disposed in parallel with each other within a reaction chamber and in which RF power is supplied to the discharge electrode from an RF power source through a matching unit, wherein two or more power supply points of substantially equal voltage are employed for supply of power. 
     
     
       17. A power supply method according to  claim 16 , wherein the number and position of the power supply points are determined such that the shortest distance as measured along an electrode between at least one of the power supply points and any point located within a portion of a surface of the discharge electrode which faces a substrate is not greater than one-fourth of the in-vacuum wavelength of the RF power. 
     
     
       18. A power supply method according to  claim 16 , wherein in order to supply RF power to a plurality of points on the discharge electrode, a first coaxial cable having an end divided to form two ends is provided as a power transmission line in order to receive an output from the RF power source; two second coaxial cables, each having an end divided to form two ends, are connected to the divided ends of the first coaxial cable, each of the second coaxial cables having a length equal to one-fourth of an in-cable wavelength of the RF power and a characteristic impedance equal to that of the first coaxial cable; and four third coaxial cables, each having a characteristic impedance equal to that of the first coaxial cable, are connected to the divided ends of the second coaxial cables.